"Prop song"...

[Rendelf]

Hi ho wondrous Canal folk.,

 

 

 

Have any of you come across the idea of "prop song"?

 

Described to me as the prop resonating through at certain RPMs, causing a wailing noise which passes through the hull.

 

Such a noise exists on our boat from about 300 to 1,000 RPM. It's reasonably loud, being heard the length of the boat, and over the engine. It seems to emanate from the gearbox end of the engine / back of boat. Noise not present in neutral or reverse.

 

Does this sound like the sort of thing that could be causing the noise, or are there any other thoughts about what it might be?

 

I can live with the noise until we black the hull (apparently at that point the prop can be re-edged?) but slightly concerned it could be something worse.

 

Thanks in advance!

[dave moore]

This is a well known phenomenon that affects some boats. The usual remedy is to adjust the edges of the prop blades with an angle grinder and linishing disc, preferably by someone with experience of the issue. If you could remove the prop for treatment it would save any slipping or docking charges. I'd approach a good, old fashioned boatyard for help with this one.

 

Dave

[nicknorman]

In my limited experience prop singing occurs over a very narrow rpm range. In our case it was 1200 to 1300 engine rpm. You are talking about a more than 3:1 rev range which makes me think it isn't.

 

The sound is a sort of metallic screeching noise. The pitch doesn't change with a change in rpm.

 

Anyway if it is singing, putting a chamfer on the trailing edge of the prop is the solution.

[Rendelf]

In my limited experience prop singing occurs over a very narrow rpm range. In our case it was 1200 to 1300 engine rpm. You are talking about a more than 3:1 rev range which makes me think it isn't.

 

The sound is a sort of metallic screeching noise. The pitch doesn't change with a change in rpm.

 

Anyway if it is singing, putting a chamfer on the trailing edge of the prop is the solution.

 

 

I'd describe ours as more of a wailing noise, which wobbles slightly at the same rate as the engine noise. (You can hear our Isuzu 42 turning over at lower revs) It increases in volume as the revs increase, but does not change pitch.

 

 

 

This is a well known phenomenon that affects some boats. The usual remedy is to adjust the edges of the prop blades with an angle grinder and linishing disc, preferably by someone with experience of the issue. If you could remove the prop for treatment it would save any slipping or docking charges. I'd approach a good, old fashioned boatyard for help with this one.

 

Dave

 

 

Any recommendations for such a boat yard? We're currently heading south on the Oxford, intending to follow the Thames to London and then the GU to Birmingham. That said, the boat does have to come out this autumn for blacking.

Edited July 6, 2016 by Rendelf

[cuthound]

Our second share boat suffered from this when new.

 

The builder suggested leaving it until the end of its first season, as sometimes it cures itself as the prop hits things in the cut, taking the edge off the blade.

 

After about 500 hours it cured itself.

 

Of course 500 hours in a shareboat takes a lot less time to clock up than on most private bosts.

[nicknorman]

I'd describe ours as more of a wailing noise, which wobbles slightly at the same rate as the engine noise. (You can hear our Isuzu 42 turning over at lower revs) It increases in volume as the revs increase, but does not change pitch.

 

If it gets significantly louder with increasing rpm, again this doesn't sound like classic prop singing. Could it be some resonance in the prop shaft/stern bearing area? Does it have a conventional stern tube with greaser? If so, does turning on the greaser a couple of turns make any difference?

[Rendelf]

If it gets significantly louder with increasing rpm, again this doesn't sound like classic prop singing. Could it be some resonance in the prop shaft/stern bearing area? Does it have a conventional stern tube with greaser? If so, does turning on the greaser a couple of turns make any difference?

 

That was kind of my suspicion too, although the noise is not apparent when in reverse, even at quite high revs. Boat has a conventional stern tube/greaser. When we first bought her the stern gland was leaking. Upon inspection, it was apparent that there was no packing inside - box was just full of grease. Though I can't recall the exact changes, I'm sure that the boat didn't sing like this to begin with - though prop song can both develop and stop with collisions to the leading edges - as I understand it.

 

 

 

I'll have another listen when I next move and try the greaser as you suggest.

[Scholar Gypsy]

I've had this issue for a while - very narrow RPM range, so not a big concern. I might get the yard to get the angle grinder out when the hull is blacked this winter.

 

One upside is that it's a neat way of detecting if there is anything on the prop - even the tiniest bit of weed is enough to disrupt the whine ...

[nicknorman]

I've had this issue for a while - very narrow RPM range, so not a big concern. I might get the yard to get the angle grinder out when the hull is blacked this winter.

 

One upside is that it's a neat way of detecting if there is anything on the prop - even the tiniest bit of weed is enough to disrupt the whine ...

Our boat no longer "sings" in fwd - the builder sorted it with a grinder after our first shakedown cruise. However it does sing a bit just above idle in reverse and I now find this noise comforting and reassuring because, as you say, it indicates that the prop is clear. If it doesn't do it, there is something on it!

 

Just to pick up on something the OP said, it is the trailing edge that 'sings' and so collisions in fwd are unlikely to affect it, it is collisions in reverse that might.

Edited July 7, 2016 by nicknorman

[Paringa]

Old skool skippers would run a singing prop through some gravel in the hope the resultant dings would be enough to upset the harmonics...which is all you are trying to do.

 

Also "singing" brings to mind some lovely melody, it can sound awful like some mechanical failure and very annoying if it is in your cruising rev range...like mine at gear engaged speed...a whoo, whoo, whoo....drove me barmy.

 

It is a bit of a dark art to stop it, you only need to take a small amount off the trailing edge so beware getting over excited with the grinder, and the angle is like you are trying to sharpen it if that makes sense, but not to a point.

 

I used a metal file thinking I can't make it any worse and first go it had sorted it...my friend had numerous goes and ended up with a new prop.

 

The other school of thought is if you are sure it isn't a mechanical failure "just live with it" but that is easier said than done...

 

Good luck

[Greylady2]

 

 

Sorry could not resist. :-/

[Rendelf]

So those are the infamous Wiggles!?

 

I always assumed they were people in fluffy suits, like the Tellytubbies.

 

I suppose I could always cruise with that song on full blast....it might be just slightly less annoying than the prop in the middle of the cruising rpm range.

 

Perhaps next time I find some gravel, I'll reverse through! Alternatively, we plan to cruise on the Thames this summer....so could get a snorkel and a file...

 

Thanks for commments re. trailing vs leading edges.

[Greylady2]

So those are the infamous Wiggles!?

I always assumed they were people in fluffy suits, like the Tellytubbies.

I suppose I could always cruise with that song on full blast....it might be just slightly less annoying than the prop in the middle of the cruising rpm range.

Perhaps next time I find some gravel, I'll reverse through! Alternatively, we plan to cruise on the Thames this summer....so could get a snorkel and a file...

Thanks for commments re. trailing vs leading edges.

I know what you mean theirs nothing more annoying than that screaching sound that seems to come from the gearbox, it gets almost embarrassing.

 

The towpath comments 'owe their fan belts slipping'

 

A pathetic daft song would be an improvement lol.

[Tony Brooks]

Old skool skippers would run a singing prop through some gravel in the hope the resultant dings would be enough to upset the harmonics...which is all you are trying to do.

 

 

As the OP said they were heading to the Thames I was gong to suggest they try that but thought better of it in case they jambed a rock between skeg and prop. If it was mine that’s what I would try first.

[Paringa]

Yes so easy to turn one problem into several other usually bigger ones...

 

If the OP is spending some time on the Thames feel free to contact me and we might be able to get to the grid at strand on the green...A tidal drying out spot and a brilliant facility.

 

If not a a swim with a metal file in some fine weather sounds like a way to spend a afternoon!

[Tony Brooks]

Or try using an large F type adjustable spanner down the weed hatch to put a slight kink in the tip of one blade.

[Rendelf]

Thanks all!

 

There are lots of solutions here.

 

I think I'll have a little go with a spanner through the weed hatch....could feasibly get a file in there too....or use Mrs R's little hands. Then I'll get my goggles on, and swim on a sunny day. Failing that, could check out the grid in London and use the anglegrinder.

 

As the range is 300 - 1,000 rpm...do any of you have suggestions for eliminating the gear box/prop shaft as the cause?

 

There is no song in neutral or reverse, even at high revs. The song does seem to emanate from the prop shaft bilge/stern gland/gear box area...but if it were the prop I imagine this would remain the case.The noise increases in volume with rpm, but not tone; it 'throbs' along with the engine.

 

If I can't alter the parameters of the noise by dinging/spannering/filing...then I suppose I've eliminated the prop.

 

Thank you for suggestions!

Edited July 8, 2016 by Rendelf

[Scholar Gypsy]

I did "cure" the problem by putting a cable tie around the foot of one of the prop blades. It lasted for a few days, but did demonstrate beyond doubt the cause of the problem.

[Tony Brooks]

 

As the range is 300 - 1,000 rpm...do any of you have suggestions for eliminating the gear box/prop shaft as the cause?

 

 

 

The best you can do is use a listening stick or very long screwdriver to test various parts of the gearbox and stern gland. One end (handle end) against ear and touch the other end on likely sources. Normally the sound will be the loudest closest to the problem.

 

About the only think in the gearbox I think is likely to cause this sort of sound would be a worn/damaged/incorrectly shimmed ahead gear thrust bearing but that depends upon the design and f you have some kind of thrust block on the shaft.

[Albion]

The correct method, which works, is to grind the rearmost edges of each blade down at about 30 degree angle starting just below the tip curve on the leading edge of each blade, round the tip and finishing about half way down each trailing edge. This is the method used by Jooren in Holland (well respected manufactures of props: http://www.scheepsschroeven.nl/uk_bedrijf.html)

I have once done it with a file working through the weed hatch of my barge but it took two attempts to cure it completely and about 4 hours of hard work in total.

Roger

Edited July 8, 2016 by Albion

[gbclive]

I did "cure" the problem by putting a cable tie around the foot of one of the prop blades. It lasted for a few days, but did demonstrate beyond doubt the cause of the problem.

I have a similar problem to the OP.

A replacement slightly smaller prop has recently been installed with less pitch that solved nicely the origional prop that caused the Kelvin J2 to labour.

No problem until subsequently a crude overheating mid prop shaft support bearing was replaced with a nice new pillow bearing.

We now have a steady high pitched tone between about 450 and 600 RPM, which inconveniently is in the middle of our cruising RPM range.

I have used an engineers stethoscope but no success in identifying the place where the noise eminates from. Just generally from the aft end, but can just be heard from the bow.

The respected marine engineer who installed both the prop and mid bearing has nicked the blade leading edges with a file via the weed hatch - but no improvement.

Can I check please that the propeller "foot" is the narrow root of a single blade?

Thanks.

[Rendelf]

A little update...

 

I have found a good way to eliminate the other bits of the boat as the cause of the noise!

 

Today, after some incredibly skilful helmsmanship -- which saw me having to fishtail the boat and then throw her hard astern in order to collect my crew -- I heard a clunking noise, and felt the tale-tale sloshing noise of something wrapped around the prop. After a few minutes, I realised that there was no longer a wailing noise! We were so happy that we kept our new passenger, until a bridge and a blind bend produced an oncoming shiny green boat. Another full reverse session freed whatever was around the prop.....and the wailing returned.

 

Still. Now we do know that the song is indeed singing from the prop. File and snorkel at the ready!

[Scholar Gypsy]

The correct method, which works, is to grind the rearmost edges of each blade down at about 30 degree angle starting just below the tip curve on the leading edge of each blade, round the tip and finishing about half way down each trailing edge. This is the method used by Jooren in Holland (well respected manufactures of props: http://www.scheepsschroeven.nl/uk_bedrijf.html)

I have once done it with a file working through the weed hatch of my barge but it took two attempts to cure it completely and about 4 hours of hard work in total.

Roger

 

Dear Roger

 

Many thanks for this advice. I spent about an hour with a hand file on my prop this morning, while it was out of the water, reducing the thickness of the edge of the blade by about 50%. It worked a treat!

 

I have a new problem, which is that for many years normal cruising speed (rivers and canals) has been "just above the whine". I am finally going to have to get the rev counter fixed, or find some other way to decide the speed I like.

 

One photo below, showing where I ground the first blade. More photos here. Thanks again

 

[Albion]

As long as the grinding is done thoroughly and takes enough off (and around each tip exactly as you have done in the picture) it is a guaranteed cure. I have used the method on several of my props now. Jooren normally send out their props with the grinding already done straight from the factory but, on one occasion, it wasn't quite enough and hence the 4 hours working through the weed hatch with a file. It is SO much easier to be able to get at the prop in a dry dock of course and even easier with an angle grinder.

Roger

[PeterDHS]

Excellent photo....shows exactly what is needed. Hope it has permanently cured the dreaded whine !!.